In recent years, to improve color reproduction of an image sensed by an image sensing apparatus such as a digital camera, more complex image processing is used to convert image data, which is obtained by A/D-converting an image from a CCD, into a final output image. Examples of the image processing are color conversion processing corresponding to chromatic adaptation as a human color perception characteristic and color conversion processing for converting a color into a memory color that is felt by humans as desirable.
The present applicant has developed a processing method using a three-dimensional lookup table for the above image processing. However, in the color conversion processing corresponding to chromatic adaptation, to change color reproduction in accordance with a change in photographing light source (color temperature), three-dimensional lookup table data equal in number to light sources corresponding to photographing light sources (color temperatures) must beheld, as shown in, e.g., FIG. 4 of Japanese Patent Laid-Open No. 8-9241. However, the size of the three-dimensional lookup table data is very large. To hold a plurality of three-dimensional lookup table data, the memory capacity in the image sensing apparatus must be increased. To hold three-dimensional lookup table data equal in number to light sources is not realistic from the viewpoint of cost. There is another method in which three-dimensional lookup table data equal in number to a minimum number of light source color temperatures are held, and at the time of photographing, interpolation arithmetic processing corresponding to the light source color temperature at that time is executed using the three-dimensional lookup table to create three-dimensional lookup table data corresponding to the light source color temperature. However, the less the number of three-dimensional lookup tables becomes, the lower the color conversion accuracy becomes. In addition, since at least two three-dimensional lookup tables are still necessary, the memory capacity must also be increased.